This invention relates to space heaters and, more particularly, to space heaters of the direct air combustion type that provide for recirculation of indoor air and for the bypass of some of the fresh air drawn over the burner.
An example of a space heater of this type is disclosed in U.S. Pat. No. 4,429,679 issued Feb. 7, 1984 to James V. Dirkes. The space heater disclosed in this patent includes a direct air burner suspended in a first air passageway or chamber located adjacent to a second air passageway or chamber. Both chambers communicate with a mixing chamber in which is located a blower that discharges air through a discharge opening into the building to be heated. The first chamber has a fresh air inlet opening that is provided with an adjustable damper that is open when the heater is operating and closed when it is not and that communicates with a fresh air intake. The second chamber has a fresh air inlet provided with adjustable dampers and it also communicates with the fresh air intake. The second chamber also has an indoor air inlet provided with adjustable dampers and this inlet communicates with the inside of the building being heated.
The blower pulls the air it discharges from the outside and also recirculates some of the indoor air. Safe operation of the space heater requires that a minimum of 20% of the air discharged into the building be drawn over the direct air burner to insure complete fuel combustion. The remaining 80% of the air discharged into the building is a complementary composite of fresh, unheated air and recirculated indoor air pulled through the second chamber. By providing the complementary composite, the air pressure inside the building can be maintained higher than the outside air pressure to prevent infiltration of cold air into the building.
The complementary relationship between the fresh unheated air and the recirculated indoor air is accomplished by conventional mechanical interconnecting means associated with the adjustable dampers in the second chamber inlet openings. The mechanical interconnecting means is arranged such that as one damper opens, the other closes and it is controlled by a pressure sensor inside the building.
Space heaters of the type disclosed in the Dirkes patent cannot account for variations in air flow over . the burner. Such variations can result from changes in outside air pressure caused by changes in the wind, changes in recirculation flow caused by closing or obstructing the recirculation ductwork and variations in supply air through over-pressurization inside the building or the throttling of supply air volume.